Sweep generation



July l0, 1951 R. M. PAGE SWEEP GENERATION Original Filed Sept. 19, 1942 Om wm ROBERT M. PAGE Patented .ul-y 10, 1951 2,559,657 sWEEP GENERATION j Ruhen Page, Wasiiiigttn,"n,V C.

originaiapplicauml-Y september 19, 19412,Y serial No. 459,010.y Divided andths applicationAu` gust 27,1947, serial No. 770,842

1-4- olaims. (C1. 315;"24)l` (Granted undertiie act of .March-I 3; 1883,@ as1 amended-April 30; 1928;- 370 OVG.- 757-) 1`- This-inventionrelates-to `radio echo apparatus andv more; particularly toi methods of andv means for detectin'g'- the presence oiremote objects includedwitliina--field-lexteridin'g!3609 about aref'- eience' point and-foi` producing! a visual plan positionindication-off such area' whereonv detecte'd-reinote` obj ectsarefindicatedin such a manner as-v to si-mul-taneo'usly4 showy range' and direction thereof;

-Radio echo apparatusesdisclosedby the prior art includeadirectional beam antenna-"from which-equally spaced energy pulses are emitted ati a'- c'onstantrate,` and ani indicator, suchasz a cathode' ray" oscillograph; upon which `atime sweep is impressed in synchronismwith the energy pulses'emitted fromthe antenna. Whenthe-emitted? energy pulses impinge upon remote objects-echopulsesare reflected from` the "objectsandlapplied-to' the'indic'a'to in sucha-manneras tp'rduce'- an'-A indication on the sweep which por; trays a measurement of range v'off the-remote ob` ject-fro'mlwhich -the-"echop'ulse reilected.- In :the priori systems directional--indications1 of remote' objects-detected inthe foregoing manner are derived froin'itheangular position of the directional beam antenna-- Directional indications obtained in this'mann'erarenotiof a'high degree-o'-accur'acyfsin'ce'` the directional' energybeamemittedfrom the antenna must necessarily ha-ve sub`- stantial Widths, approximately equal to-anarc-of 107' to 151degrees-.andechfpulse indications are therefore produced on the Iindicatorwhenever a1 remote objectfis includedwithin anyr portion of the beam'.- Consequently, it-b'ecomesnecessaryto continuallyfadjust the-antenna bearing until-echo pul'selindicationsof maximum amplitude" are-pro-A duced; which case it -isassumed that the -middle of the'directional energy-beam,- thev portion thereof having the greatest'v power, is directedtoward-theV object, and also thatthe' antenna-is likewise pointing..directly towardA the object. The latter oper-ationsare` extremely. dii'cult to perform'rapidlywith a-high degree of accuracy-andv of'. a remoteobject' corresponding` yto a` remote -1 nennen when attempting-'tddetermmefrang ,2j object indication produced onthe -indica-toi* since the means -fo'rr indicating-'range:andrea t are-distinct? isolatedlllevices;` DCulties-aiisi' be'caus'eof" the latten-are' more readiIy'compr-i 'ndi approximate bearing'inclicationsg-tne failaoiesedt' thi'e-fore'goingnA method areobvious, especially iii instances wherein theremotef objects `arefm'ovin'e; at' high-=velccitie's, @such vras"'aircraft, lf'or example-' Itis thereforev an' object orthe'` present inven: tion to 1 provide-aI novel! niethoc'i for' indicating;- Iallgearid dii-eC-'tinof remote Objec'ts f Another object is to provide nove1l\meaiis"for indicating range fand* direction -of remote objects;l

Another objet-,tv is to-` provide novel 1 means :for simultaneously indicating range'v and direction i ofremoteob'jec'ts onan oseillo'graph by. usefofse-" arate c'ooil-climates:-4

Another object4 is yto' .provide far-novel?- radio' echo apparatus for' producing=^ a planf position indica tion off remote-'objects-includedwithin a 'fieldiex-e terioliiigiSGOQ abouti-the'apparatus,:With'itheindi cation of`v each object simultaneously showin-"gv range 'and' direction thereof. l

Still another obj ecty off the present: invention-is to. provide a? novelA method for-"pro'ducingiavv rotat= ingiv radialsweep.z 'ofthe-'electron beam ofan-o'scili-f lograph.-- Y

Still'- another-f'obj ect i isL Lto' :pro-Vide` a--ra'dio' ecli'o apparatus1includingnovelfmeans for-producinaf radial 2 time swe'ep; 1 of-'i the"- ei'ectron f b'eamlfof-T an oscillog-raph andi' forlr'tatingfthei'sweep -iin' syn# chronismwith rotation off anten'narof thai-appa"4 ratus whereby! rangel affidd-ire'ctional-` indications of :remote objects included *with-in'a'neld'extende" ing 360 about thefapparatus'aresiniultaneousli obtained frn the;` indications vproduced on" the os'cillograph.

.Still ano'tlier object?. is" -to'fprovide noyelelectrm' magnetic' meansl '.for producingea'frtatingf radialy sWeep-of the 'electi'on ibe'arri )of-1an" osi-li'o'grapn.`

Stillvanother object is to provide' -a radiof-` echa apparatus vln'tfving-.an oscllogfaph'with-'meansiorf producing -a-rotatina radial-:sweep V"of Y theV electron4 3 beam thereof, including novel means for varying the point about which the sweep rotates.

Other objects and features of the invention will appear more fully hereinafter from the following detailed description when considered in connection With the accompanying drawing which discloses a radio echo apparatus embodying the principles of the present invention. It is to be expressly understood, however, that the drawing is designed for purposes of illustration only and not as a definition of the limits of the invention, reference for the latter purpose being had to the appended claims.

It is contemplated by the present invention to produce a highly directive beam of energy, such as a series of equally spaced radio frequency pulses, which is continually rotated to scan an area extending 360 about a reference point with the directive energy, and to produce a radial sweep of the electron beam of an oscillograph which rotates about a fixed point on the oscillograph screen in synchronism with rotation of the directional energy beam. The rate of emission of the directional energy is synchronized with the radial sweep of the electron beam so that energy reflected from remote objects included in the scanned area produces indications on the sweep, at certain distances from the rotating ends thereof, which are direct measurements of range of the remote object from which the energy reected, while the angular position of the sweep, at the instant a reflected energy indication is produced thereon, represents the direction of the remote object. With an apparatus having the foregoing characteristics, a visual plan position indication is produced on the oscillograph screen which portrays the remote objects included within the scanned area, at certain radial and langular positions with respect to the center of the oscillograph screen in a manner corresponding to the` range and direction of remote objects with respect to the apparatus. An indication of the foregoing type is disclosed and described more fully in the application of Robert M. Page, Serial No. 455,582, filed August 21, 1942, for Radio Echo Apparatus, now abondoned.

With reference more particularly to the drawing, the radio echo apparatus constructed in accordance with the principles of the present invention that is disclosed therein includes directional beam antenna I0, pulse transmitter II and pulse receiver I2. Transmitter II and receiver I2 are connected to antenna I0 by means of duplexing circuit I3 which automatically functions to form individual connections between the transmitter and the antenna, and between the antenna and the receiver so that a single antenna is employed for transmission as well as reception. The output of transmitter II is modulated by electronic keyer I4 in such a manner that the former produces equally spaced energy pulses, such as radio frequency pulses, at a rate determined by synchronizer I5 which controls operation of keyer I4, which are emitted from antenna I0 in the form of a directional energy emission. Energy received at the antenna is passed through receiver I2 and coupling condenser I6 to control grid I1, of oscillograph I8, to modulate the intensity of the electron beam of the oscillograph. Antenna I0 is rotated, in a horizontal plane for example, by means of motor I9 throughshaft 53, so that the directional energy pulses omitted from the antenna may be scanned overanarea extending 360 about the antenna, or through anydesired angle. Antenna I0 is to 4 be of any suitable construction capable of prducing a highly directive energy emission, and transmitter II and receiver I2 are designed in such a manner as to properly transmit and receive pulse energy, such as transmitters and receivers employed in conventional television equipment. oscillograph I8 is of conventional construction in so far as the same comprises an evacuated cylindrical envelope 20 having a viewing screen, not shown, at one end, with electron emitting means mounted in the other end thereof. The electron emitting means includes cathode 2l, heater element 22, grid 23 and anode 24, from which the electrons are emitted at extremely high velocities toward the viewing screen. As mentioned heretofore, it is an object of the present invention to provide novel electromagnetic means associated with oscillograph I8 for continually radially deflecting the electron beam emitted from cathode 2I in synchronism with ther pulse energy emitted from antenna I0 in a direction corresponding to the direction of the pulse energy emission from the antenna. As shown in the drawing, ,the foregoing means comprises cylindrical coil supporting member 25 mounted for rotation about the outer periphery of envelope 20 by means of anti-friction bearings 26 which cooperate with member 25 and race member 21; the latter member being securedto the outer periphery of envelope 20, between the electron ybeam emitting means and the oscillograph viewing screen, by any suitable means. Deflection coils 28, 28 are carriedby member 25 and are electrically connected to slip rings 29 and 30 through conductors 3| and 32. The aforementioned means also includes saw-tooth wave generator 33 of conventional design to produce saw-tooth varying currents, as well as a source of constant direct current, the purpose of the latter will appear more fully hereinafter. Synchronizer I5 is connected to generator 33 to control operation of the latter in such a manner that generation of saw-tooth current wave forms are initiated at the instant an energy pulse is generated at transmitter I I. The output of generator is fed to deflection coils, 28, 28 through conductors 34 and 35 which respectfully terminate lat contacts 36 and 31 slidably mounted on slip rings 29 and 30.

Deflection coils 28,V 28 are diametrically mounted in supporting member 25 and are wound in such afmanner as to produce a uniform uni-directional electromagnetic field therebetween, that passes through envelope 20, when a source of direct current is applied thereto. Application of saw-tooth currentwave forms to the deflection coils produces uniform electromagnetic fields between the coils, the strength of which varies at a constant increasing rate, from a field of zero strength, at the originating point of the sawtooth wave forms, to a field of maximum strength when the saw-tooth wave forms attain maximum current values. The electron beam emitted from cathode 2I normally moves along the central axis of envelope 20; however, when a saw-tooth varying electromagnetic field is applied between the deflection coils; the electron beam is deflected, in a direction at right angles to the direction of the electromagnetic field, by an amount directly proportional to the strength of the field. It is to be expressly understood, therefore, that the electron beam is radially moved from the center of the oscillograph screen upon application of each saw-tooth wave form to the deflection coils. When as eries of saw-tooth current wave forms are applied to tlreadeflectionf-coils; a constant direct current/the.- average current value of; the. saw-tootlfi.V wave l forms, produces.: a constant electromagneticfeld'.betweem the coils.. Theconstant iield tendsto .'maintaintheelectroni d beami at some position .remoteirom the central. axis-.oenyelope 2Q.. Since, as mentioned here@ tofore, an` object of? the presenti inventioni is' .tol produce'. a radial sweep of'. the'. electron beaml thatv is, a .sweepthat originates at the' centerof' 10.

the oscillograph. screen; a source. of. direct-f cur.- renttislalso applied to the. deflection; coils; byfway; of conductors 34 and 35, of the proper polaritys tb.;'.produce anv electromagnetic fieldifin oppositiomtothe'constant fleldi'produced bytheafore.- 15-f mentioned: Vaverage direct'. current: Withi the. foregoingarrangement the :electron .beam isradi1- l ally; movedlfrom.. the., centen of' the: oscillograplr; screen@ upon` applicationA of 'eaclr saw-tooth cur-- rente' waye. form. 201;

In order to rotate the radial sweep of'theelectronheam. in synchronism'. with rotationof antorina; lil: in. such ai manner; that the electronbeam continually moves: ina direction correrA spending tothe direction ofaemission'of the'. die 251 rectional energy from the.antenna,.means are. Inici/idoli forsynchronizing. the angular positions ofzcoilj. supportingV member. 25. and antenna.; HL., anidzfcrfrotatingthe member andthe antenna in. such' aimannerasto continually maintain-such. 30 synchronousangular; relationship. As. shown, the'` foreeoingmeanscompris'es annular gear 3.3 se cured to; the outer' periphery of l coil. supporting member v2,5 at one end thereof, and pinion 39; ro

tatably connected to motorsl'through shaft' 4G', 35

which; cooperates with annular gear' 38; The drivingyconnections between motor i9 and antenna |D, and between the..motor-anducoil` sup-f porting.; member 25,. are'` so;v designed that coil supporting member-251 rotates through va com'- y iol` plete revolution during the timerelqriired;toA ro..- tateaanten-na. ill throughout, 360i; while-the. coil supporting membenisfangularly positioned; about` the oscillograph, in such a manner that the elec.- tronbeam moves in a direction corresponding to., the direction of emission ofthe directional ener-4 gy from 2 thef, antenna.

Asftpleviously mentioned,y means are provided; ba@ thepresent invention; for. varying the' point;

abont.which the radalisweepr of tneelectron 50A beam rotates to any desiredfpositionwithinior: outside-the oscillcgraphgscreen; By 'varying the point,.aboutf which .the radial sweep rotates, and:` by.v expanding the lengtlr of: the sweep, any; def sired-porticn of 2 the arearscanned;I bythe direc?"` f tionalene-rgy emitted :from the; antenna may bef; indicated on the ,entire l area of the oscillograph screen. WithY an arrangement. having: f th'exioree going characteristics, indications of objects;.at1 extreme. remote/positions .with respect to. the apparams;Y areobtained in suchY a ,mannerg that: range and directional indications thereof.; are'. rapidlyobtained 4With.-a,higlfi degree of faccuracy, asewillfappea-r more fullyfhereinafterr Theoregoing Ameans. fcon'iprises .cylindrical-coil supporting.: member Y4i rotatably mountedtabout s. ther-outer peripheryof member' 25v by means lof anti.- .friction1.bearings 42; Member; 4 li; is Avrotatecli uponimanuall movement of knob-z 43.*whicli is secured topinion 44?, Whilefthelatter elementfco- 70 oneratesiwith Aannular gear r 45.: mounted on the. olrteri'periphery-A ofmember: 4.1 Deiiection .coilse 46.;, 4Bzfarcarriedby. mem-ber 4i inf diametric relation, andfiare wound inl-suchf-a manner esito'- preduce a1uniform.uni-directional electromag` 75 notie. feldi betweenv the :coilsfand; through erle Velopef-Zv,.when a' source of directv current'. ist appliedl to ther coils. The deflection coilsl arci connected-v to slipl'rings 47! and' 48/Ycarried by* member' 4| rent supply 49` is fedI to deection. coils 46, 461i. through: conductors: 50: and 5l, each` of whichv terminate incontacts'` that' cooperate with slip!v rings;41and. 48. When it. is-desiredito movethe';` point about' which'. the radial sweepof.` the elec'- tron. beam rotates, the output of` supply 49 is'v regulated until= the: directl currentLied' to coils-46.l. 46:.' produces an electromagneticv iield. ofy sucient;I strengtlrto deflect the electroni beam of the' oscillograph the desired'` amount from the' centerA oiV theoscillograph screen.. Member lliv is then'.` rotated, uponzmanualm'ovement' of; knob: 43;.t'o1'- Vary-A the.V direction. that; the electron` beam. isi moved until the desired. angular. positionlthereof isobt'ained` In ordertolexpand the radial sweepi ofi theelectron beam; theamplitudeo the-Sawhtooth; current. wave: frmsufrom'.. generator 33 isi increased upon adjustment.. of. control. 52' asso'.-- ciate'd with the generator.

A's mentioned' heretofore; transmitter IIf' proav duces a series of equally spaced energy pulses;l such/as radio frequency pulses,v upon operationof keyer `l4;.at a rate controlled'by'synchronizer l5; which.` are emitted; from antenna I 0i in" the form"l of a. highly directive energy' pulse emission: Synchronizer vl 5 also. controls operation' of' saw.-I toothr'generator 33 rin such aimanner. that. genera'- tionjof a saw-tooth current Wave form isiniA tiatedat the instant an-energy pulse-is generated atl the'transmitter. The saw-tooth Varying cur rent-.output,as well asa source'. of direct current, from' generator 33-is applied to deflection coils 2.8,. 28- to produce al uni-directional saw-tooth varying. electromagnetic e'ld within` envelope.20= which radially deflects vthe electron beam emitted.. from.. anode. 24,v upon. application ofV each sawtooth wave form `to the coils. Since antenna. lll.. and coil supporting member` 2'5 kare synchronously rotated upon operationof motor I9, the electron. beam continually radially sweeps in a direction. corresponding tothe direction thattheenergy. pulses are emittedv from the antenna.

When antenna Illis'continually rotated to scan. an area extending 360 about' the antenna with. the directional'energy emission, the energy pulses impin'ge upon' and'reect from all remote objects.. included within the 'scanned'area The reflected energy pulses'are received'at'antenna Ill', passed. through receiver I2" and' applied to control'grid I'l-'of oscillograph |81 by' wayi'of condenser I6, to' modulate the intensity'ofthe'electron beam thus' producing a visual indicati'on ony the'oscillograph" screen.- Since thel electron'beam^ initiates' radial movement inl a-direction corresponding to the` direction ofthe pulse'energy emissionfromthe; antenna, whenever an energy pulse'- is' emitted, the electron beam is-modulated, in-responseA t reception of reflectedenergy pulses correspond# in'gfto-the energy pulse emitted atthe instantI ra'diial'movement ofthe electron beam initiated; when the same occupies a certa-inlradial: dis-'-4 tan'cef-irom-the center of the*oseillograph-'screen that istat directf measurementof range of. the#- object from which the energy pulsel reilected;y while the angular position of? theradial sweep'at thef.instant:.the indication is' produced thereon indicates thedirection, or azimuth angle, of suche objectll In =the event that' more accurate range d and-1 f directionaliiindicationssof acertain remoteobect-f The-.output of variable direct-cure detectedin the foregoing manner is desired, the radial sweep of the electron beam is expanded by increasing the amplitude of the saw-tooth current wave forms by adjustment of control 52, and supply 49 is regulatedto apply a source of direct current to deflection coils 46, 46 to produce a uni-directional electromagnetic field that deflects the electron beam in a direction' determined by the angular position of the deflection coils. The angular position of deflection coils 46, 46 is varied, upon rotation of knob 43, to occupy a position wherein the electron rbeam is dellected in a direction substantially opposite the@ direction of the remote object of which an indication is desired, with respect to the antenna, while the current fed to the deiection coils is regulated in such a manner as to move the electron beam to a new point of rotation that is sufficient distance in the aforesaid direction from the center of the oscillograph screen so that the expanded radial sweep utilizes the entire diameter of the screen. Since deflection coils 46, 46 are capable of rotation throughout 360 any remote object included within the scanned area may be individually indicated in the foregoing manner.

There is thus provided by the present invention novel methods of and means for simultaneously indicating range and direction, or the azimuth angle, of remote objects on the screen of an oscillograph, or any other suitable indicating device. The novel means disclosed and describedr herein is so characterized that a visual plan position indication of all remote objects included within an area extending 360 about a reference point is readily obtained, wherein remote objects are indicated on the viewing screen of an oscillograph at radial and angular positions with respect to the center of the screen that respectively correspond to ranges and azimuth angles of remote objects with respect to the. reference point. Furthermore, the present invention provides novel electromagnetic means for producing an extremely stable radial sweep in synchronism with rotation of a remote rotatable member with a high degree of accuracy, as well as providing other novel means for varying the point about which the radial sweep rotates to any desired position so that extremely accurate range4 and directional indications of preselected remote objects may be readily obtained.

Although several modifications of the present invention have been shown and described in detail herein, it is to be expressly understood that various changes and substitutions may be made therein without departing from the spirit of the invention as well understood by those skilled inthe art. Reference therefore will be had to the appended claims as a definition of the limits of the invention. Y

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

. This case is a division of my application Serial Number 459,010, filed September 19, 1942; for Radio Echo Apparatus.

What is claimed is:

v 1. The method of producing a rotating radial sweep of the electron beam of a cathode ray tube which comprises producing a uniform periodic linearly varying electromagnetic field across the path of said electron beam and rotating said 8 field at a frequency low with respect to the periodicity of said field.

2. vThe method of producing a rotating radial sweep of the electron beam of a cathode ray tube which vcomprises producing a uniform periodic linearly varying electromagnetic field across the path of said electron beam, applying a constant uni-directional electromagnetic field across the path of said electron beam in opposition to a constant uni-directional electromagnetic field corresponding to the average of said periodic linearly varying field, and rotating said fields in unison.

3. The method of producing a rotating radial sweep of the electron beam of an oscillograph which comprises applying periodic linearly varying currents to diametrically opposed deflection coils mounted about the oscillograph for producing a periodic linearly Varying electromagnetic field across the path of said electron beam, and rotating said field` 4. The method of producing arotating radial sweep of the electron beam of a cathode ray tube which comprises applying saw-tooth currents to diametrically opposed deflection coils mounted about the tube for producing a periodic linearly varying electromagnetic field across the path of said electron beam, applying a source of constant direct current to said deflection coils in such a manner as to produce a constant unidirectional electromagnetic field across the path of said electron beam in opposition to a constant uni-directional electromagnetic eld produced by the average current value of said sawtooth currents, and rotating said elds. n

5. An apparatus for producing a rotating radial sweep of the electron beam of a cathode ray tube comprising means producing a uniform periodic linearly varying electromagnetic field across the path of said electron beam, and means rotating said field.

6. In an apparatus for producing a rotating radial sweep of the electron beam of a cathode ray tube, means producing a periodic linearly varying electromagnetic eld across the path of said electron beam, means applying a constant uni-directional electromagnetic field in opposition to a constant uni-directional electromagnetic field corresponding to the average of said linearly varying field, and means rotating said fields in unison. v

'7. In an apparatus for producing a rotating radial sweep of the electron beam of a cathode ray tube, means applying a deection wave including saw-tooth varying currents and a direct current component to diametrically opposed deflection coils rotatably mounted about the tube for producing a linearly varying electromagnetic field in quadrature with the path of said electron beam and initiating at a point within the tube coincident with the beam, and means rotating said coils.

8. In an apparatus for producing a rotating radial sweep of the electron beam of a cathode ray tube, means applying saw-tooth varying currents to diametrically opposed deection coils rotatably mounted about the tube for producing a periodic linearly varying electromagnetic field transverse the path of said electron beam, means applying a source of constant direct current to said coils for producing a constant uniform uni-directional electromagnetic eld in opposition to a constant uni-directional electromagnetic field produced by the average current value of said saw-tooth varying currents so that.

9 the linearly varying field initiates at a point within the tube coincident with the beam, and means rotating said coils.

9. In an apparatus for producing a rotating radial sweep of the electron beam of a cathode ray tube, diametrically opposed deection coils rotatably mounted about said cathode ray tube, means applying saw-tooth varying currents and a direct current component to said coils for producing a periodic linearly varying electromagnetic eld in quadrature with the path of said electron beam and initiating at a point within the tube coincident with the beam, and means rotating said coils at a frequency low with respect to the periodicity of said field.

10. In an apparauts for producing a rotating radial sweep of the electron beam of an oscillograph, diametrically opposed deflection coilsV rotatably mounted about said oscillograph, means applying saw-tooth varying currents to said coils for producing a periodic linearly varying electromagnetic eld transverse the path of said electron beam, means applying a source of direct current to said coils for producing a uniform constant electromagnetic eld in opposition to a constant uni-directional electromagnetic field lproduced by the average current value of said saw-tooth varying currents so that the periodic linearly varying field initiates within the tube coincident with said beam, and means rotating said coils at a frequency low with respect to the periodicity of said linearly varying field.

11. In combination, a cathode ray tube including means producing a beam of electrons, a pair of diametrically opposed deflection coils rotatably mounted about the cathode ray tube, means applying a deflection wave including sawtooth varying currents and a direct current comducing a radial sweep of the electron beam,

means for rotating the radial sweep, and electromagnetic means for positionally controlling the electron beam to vary the point about which the radial sweep rotates.

13. In combination, an oscillograph including means producing an electron beam, a pair of deflection coils rotatably mounted about said oscillograph, means applying saw-tooth varying currents and direct current to said coils for radially sweeping said electron beam, means rotating said coils for rotating said radial sweep, a second pair of deflection coils rotatably mounted about said oscillograph, means applying direct current to said second pair of coils for displacing the point about which said sweep rotates, and meansrrotating said second pair of coils for varying the angular position of said displaced point.

14. In combination, an oscillograph including means producing an electron beam, a pair oi.' deilection coils rotatably mounted about said oscillograph, means applying saw-tooth varying currents and direct current to said coils for radially sweeping said electron beam, means rotating said coils for rotating said radial sweep, a second pair of ldeflection coils rotatably mounted about said oscillograph, means applying direct current to said second pair of coils for displacing the point about which said radial sweep rotates, means Varying said direct current for controlling the degree of displacement of said point, means varying the amplitude of said sawtooth varying currentsfor expanding the radial movement of said electron beam and means rotating said second pair of coils for varying the angular position of said displaced point.

ROBERT M. PAGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,535,329 MacGregor-Morris et al. Apr. 28, 1925 1,933,219 Nakajima et al. Oct. 31, 1933 2,007,380 Morlock July 9, 1935 2,098,390 llams Nov. 9, 1937 2,241,809 De Forest May 13, 1941 2,380,929 Ahier et al. Aug. 7, 1945 2,412,291 Schade Dec. 10, 1946 2,412,669 Bedford Dec. 17, 1946 FOREIGN PATENTS Number Country Date 542,634 Great Britain Jan. 21, 1942 

